1. Field of the Invention
The present invention relates to a ceramic heater and a method for producing the same.
2. Description of the Related Art
In semiconductor manufacturing equipment, when a semiconductor thin film is formed by thermal CVD or the like on a wafer using a raw material gas, such as silane gas, a ceramic heater is used for heating the wafer. In the ceramic heater, it is necessary to maintain the temperature of the wafer-heating surface at a high temperature, for example, 700° C. In order to improve film-forming properties, yield, and product quality, it is required to control the temperature distribution on the wafer-heating surface in a very narrow range.
For example, Patent Document 1 discloses a ceramic heater including a resistive heating element composed of molybdenum embedded in an aluminum nitride sintered body, in which temperature uniformity on the heating surface is improved. Specifically, when aluminum nitride powder containing yttria powder is press-formed into a shaped body, a resistive heating element composed of molybdenum is embedded in the vicinity of the center of the shaped body, and disc-shaped or ring-shaped dummy members composed of molybdenum are embedded at positions closer to the upper and lower surfaces of the shaped body. The shaped body is sintered by hot pressing at 1,800° C. to obtain a sintered body, and the dummy members are removed from the sintered body by machining. Thereby, a ceramic heater is produced. In such a ceramic heater, molybdenum carbide is formed in the resistive heating element during sintering. When molybdenum carbide is unevenly distributed in the resistive heating element, the resistance increases thereby increasing the amount of heat generation at portions where molybdenum carbide is present. As a result, temperature uniformity on the heating surface is impaired. In Patent Document 1, by sintering the shaped body in which dummy members are embedded, formation of molybdenum carbide in the resistive heating element is controlled, and the change in resistance of the resistive heating element is suppressed. As a result, temperature uniformity on the heating surface is successfully improved.